In general the present invention relates to methods for manufacturing high resolution x-ray detectors comprised of structured scintillation (fluorescent or photostimulable) phosphor which offer substantial x-ray stopping power.
The present x-ray detector technology consists of several detection methods each of which have limitations which reduce their effectiveness. X-ray screens composed of powder phosphor mixed with a binder are used in radiography; however, the thickness and thus the stopping power are limited since the screen material is optically self-attenuating and diffusive. The powder phosphors used are typically fluorescent scintillating phosphor although photostimulable phosphors (those which fluoresce after being excited by an optical source) have been used in x-ray screens.
Vapor deposited CsI:Na used in x-ray image intensifiers for real-time radiography also has limited thickness since light diffusion problems result in resolution loss. In addition, the phosphor deposition technique may result in structural stability problems beyond approximately 0.3 mm.
Cut, sawed and cleaved scintillation crystals which are used in Computer Tomography Scanners exhibit low spatial resolution. Scintillating glass or plastic fiber bundle x-ray and particle detectors used in high energy physics have poor stopping power per unit length and poor x-ray to optical conversion efficiency. The poor stopping power can degrade the spatial resolution of the detector. The poor optical conversion often requires the use of additional amplification to boost the signal strength prior to readout. An additional limitation is that as the diameter of a fiber decreases the ratio of core-to-cladding volume decreases. This further degrades the resolution and useful volume of a fiber bundle detector. The scintillating fiber bundles are not very useful for x-ray energies below 100 KeV. However, they transmit light efficiently and thus can be made very thick which results in substantial attenuation. They may also be bent or twisted so that a readout device is not directly behind the entrance face of the fiber bundle. A fiber bundle may also be constricted at one end to reduce the size of the image displayed.
The detectors described above are used in medical x-ray radiography, x-ray nondestructive testing and in high energy physics for particle detection. The scintillation materials used in those detectors, their x-ray-to-optical conversion efficiency, and their viable attenuation lengths often restrict the useful energy range of the individual detector.
U.S. Pat. No. 4,560,882 discloses the advantages of coating the phosphorescent material of an x-ray converter with a reflective substance to improve the performance. A multiple step process is disclosed in which single elements are coated and then assembled into 1-dimensional or 2-dimensional arrays.
This application discloses a method by which highly efficient x-ray converters may be mass produced using bulk materials and repetitive processes. X-ray detectors manufactured by this method can be tailored to meet stringent application requirements.